As an example of a wireless communication system to which the present invention is applicable, a 3rd generation partnership project long term evolution (3GPP LTE) communication system is described in brief.
FIG. 1 is a view schematically illustrating a network structure of an E-UMTS as an exemplary radio communication system. An evolved universal mobile telecommunications system (E-UMTS) is an advanced version of a conventional universal mobile telecommunications system (UMTS) and basic standardization thereof is currently underway in the 3GPP. E-UMTS may be generally referred to as a long term evolution (LTE) system. For details of the technical specifications of the UMTS and E-UMTS, reference can be made to Release 7 and Release 8 of the 3rd generation partnership project (3GPP) technical specification (TS), respectively.
Referring to FIG. 1, the E-UMTS includes a user equipment (UE), eNode Bs (eNBs), and an access gateway (AG) which is located at an end of a network (Evolved Universal Terrestrial Radio Access Network (E-UTRAN)) and connected to an external network. The eNBs may simultaneously transmit multiple data streams for a broadcast service, a multicast service, and/or a unicast service.
One eNB manages one or more cells. A cell is configured to use one of bandwidths of 1.25, 2.5, 5, 10, and 20 MHz to provide a downlink or uplink transport service to several UEs. Different cells may be set to provide different bandwidths. The eNB controls data transmission and reception for one or more UEs. The eNB transmits downlink scheduling information with respect to downlink data to notify a corresponding UE of a time/frequency region in which data is to be transmitted, coding, data size, and hybrid automatic repeat and request (HARM)-related information. In addition, the eNB transmits uplink scheduling information with respect to uplink data to a corresponding UE to inform the UE of an available time/frequency region, coding, data size, and HARQ-related information. An interface may be used for transmission of user traffic or control traffic between eNBs. A core network (CN) may include the AG, a network node for user registration of the UE, and the like. The AG manages mobility of a UE on a tracking area (TA) basis, each TA including a plurality of cells.
Although radio communication technology has been developed up to 3GPP LTE(-A) based on wideband code division multiple access (WCDMA), demands and expectations of users and providers continue to increase. In addition, since other radio access technologies continue to be developed, new advances in technology are required to secure future competitiveness. Decrease of cost per bit, increase of service availability, flexible use of a frequency band, simple structure, open interface, and suitable power consumption by a UE are required.